Apparatus and methods for heat loss pressure measurement

Abstract

A heat loss gauge for measuring gas pressure in an environment includes a resistive sensing element and a resistive compensating element. The resistive compensating element is in circuit with the sensing element and has temperature response and physical characteristics substantially matching those of the resistive sensing element and is exposed to a substantially matching environment. An electrical source is connected to the sensing element for applying current to heat the sensing element relative to the compensating element. Measuring circuitry is connected to the sensing element and the compensating element for determining gas pressure in the environment to which the sensing element and compensating element are exposed based on electrical response of the sensing element and the compensating element.

What is claimed is:  
     
       1. A heat loss gauge for measuring gas pressure in an environment comprising: 
       a resistive sensing element;  
       a resistive compensating element in circuit with the sensing element and having temperature response and physical characteristics substantially matching those of the resistive sensing element and being exposed to a substantially matching environment;  
       an electrical source connected to the sensing element for applying current to heat the sensing element relative to the compensating element; and  
       measuring circuitry connected to the sensing element and the compensating element for determining gas pressure in the environment to which the sensing element and compensating element are exposed based on electrical response of the sensing element and the compensating element.  
     
     
       2. The gauge of  claim 1  wherein substantially greater current flows through the sensing element than through the compensating element. 
     
     
       3. The gauge of  claim 2  wherein a sensing current flows through both the sensing element and the compensating element, and a separate heating current flows through the sensing element. 
     
     
       4. The gauge of  claim 1  wherein the gas pressure is determined based on heating current through the sensing element and resulting voltage across the sensing element. 
     
     
       5. The gauge of  claim 1  wherein the compensating element is in series with a non-temperature-sensitive resistive element. 
     
     
       6. The gauge of  claim 5  wherein the electrical source applies current to heat the sensing element to a temperature at which the resistance of the sensing element matches the combined resistance of the compensating element and the non-temperature-sensitive resistive element. 
     
     
       7. The gauge of  claim 1  wherein the electrical source applies current to heat the sensing element to a temperature at which the resistance of the sensing element matches the combined resistance of the compensating element plus a constant number of ohms. 
     
     
       8. The gauge of  claim 7  wherein the compensating element is in series with a non-temperature-sensitive resistive element. 
     
     
       9. A method of forming a heat loss gauge for measuring gas pressure in an environment comprising the steps of: 
       providing a resistive sensing element;  
       providing a resistive compensating element in circuit with the sensing element and having temperature response and physical characteristics substantially matching those of the resistive sensing element and being exposed to a substantially matching environment;  
       connecting an electrical source to the sensing element for applying current to heat the sensing element relative to the compensating element; and  
       connecting measuring circuitry to the sensing element and the compensating element for determining gas pressure in the environment to which the sensing element and compensating element are exposed based on electrical response of the sensing element and the compensating element.  
     
     
       10. The method of  claim 9  further comprising the step of providing the sensing element with substantially greater current than the compensating element. 
     
     
       11. Method of  claim 10  further comprising the step of providing a sensing current through both the sensing element and the compensating element and a separate heating current through the sensing element. 
     
     
       12. The method of  claim 9  further comprising the step of determining the gas pressure based on heating current through the sensing element and resulting voltage across the sensing element. 
     
     
       13. The method of  claim 9  further comprising the step of connecting the compensating element in series with a non-temperature-sensitive resistive element. 
     
     
       14. The method of  claim 13  further comprising the step of providing current with the electrical source to heat the sensing element to a temperature at which resistance of the sensing element matches the combined resistance of the compensating element and the non-temperature-sensitive resistive element. 
     
     
       15. The method  claim 9  further comprising the step of providing current with the electrical source to heat the sensing element to a temperature at which resistance of the sensing element matches the combined resistance of the compensating element plus a constant number of ohms. 
     
     
       16. The method of  claim 15  further comprising the step of connecting the compensating element in series with a non-temperature-sensitive resistive element.